Protection of data communications is a critical feature of modern telecommunications networks to ensure safe and reliable data transmission in the event of the failure of a network component. In older Time Division Multiplexed (TDM) networks, various methods for protection were used. An effective method of protection in TDM networks is 1+1 line protection, where, in addition to the first line used to carry voice signals, a second line is used to provide redundancy in the case of a failure in the first line. The first line is called the working line, and the second line is called the protection line. However, this type of protection cannot be applied directly to packet-based networks, since 1+1 line protection uses two permanent lines to carry the first and second set of voice signals while a phone call is made, whereas data packets in a packet-switched network typically travel along many different routes between the source and destination devices.
Multicast is commonly used in packet-based networks to provide data communications protection, where data packets are duplicated for transmission on two ports on a target network device, the target port and another port designated as a protection port. In the event that a failure is signaled to the target network device that a fault such as Loss of Signal, Loss of Frame or Bit Error Rate, has occurred downstream from the target port, the network devices use the data from the protection port. FIG. 1a illustrates a typical prior art system 10 for 1+1 protection of data communications in a packet-based network, where a source network device 14 is connected to a target network device 22 by connection 16. In FIG. 1a, the source network device 14 is implemented as a network processor 14 labeled “NP”, and the target network device 22 is implemented as a packet-switching device 22, labeled “SWITCH”.
There are several methods of multicast protection. One form of the multicast protection is to duplicate each packet on the source network device 14 and to send the original and duplicated packets to the associated target and protection ports respectively. The packets are placed in queues (not shown) for the target network device 22, where the target network device 22 transmits the original packet from the target port 24 via connection 26, and the duplicated packet from the protection port 28 via connection 30.
However, this system requires a powerful source network device (network processor) 14 and twice the bandwidth between the source network device 14 and target network device 22 for 1+1 protection.
In an alternative multicast protection system, packets are not duplicated at the source network device 14, but instead they are duplicated at the target network device 22. Corresponding headers are added to the incoming packet by the source network device 14 so as to inform the target network device 22 to which ports of the device the packet has to be distributed, and the packet is added to a queue for transmission to the target network device 22. At the target network device 22, the multicast packet is duplicated and sent to the target port 24 and to the protection port 28 in case of 1+1 protection.
This method of data communications protection requires a less powerful source network device 14 than the previous method, however as the queue for the transmission between the source network device 14 and target network device 22 is being used for various multicast packets from different sources, contention for buffering on the queue may lead to network performance problems, e.g. may result in jitter for individual data streams such as video or loss of data due to congestion.
Accordingly, there is a need in the telecommunications industry for further development of a cost-effective method for the protection of data communications in packet-based networks which would be more efficient and reduce or eliminate network performance problems.